Layer resistance unit for voltage dividers

ABSTRACT

A layer resistance unit for voltage dividers adapted particularly for tuning or adjusting high frequency circuits capacitance diodes, said unit comprising series-connected main resistance elements at least some of which are connected in parallel with a side resistor and the latter being adapted to be varied so as to adjust the resistivity of the resistance unit to a desired characteristic, said main resistance elements and said side resistors being interconnected by conducting transverse or cross strips of conducting material. Said side resistors are adapted to have their resistance varied by progressively reducing the width of their current conductive layer surface. At least one main resistor having in addition to its side resistor connected to it in parallel a further layer resistance, all resistance layers of the unit i.e. main resistors, side resistors and parallel resistors having the same specific surface resistivity.

United States Patent [72] Inventor Josef K'dltler Bad Neustadt, Saale, Germany [211 App]. No. 779,010 [22] Filed Nov. 26, 1968 [45] Patented Aug. 31, 1971 [73] Assignee PREH Eleklru-Feinmechanische Werke,

Jakob preh Naehf. Bad Neustadt, Germany [32] Priority Dec. 1, 1967,1 11). 20, 1968, Apr. 18, 1968 [33] Germany [31] P16653973,?1665413.0andPl765 [54] LAYER RESISTANCE UNIT FOR VOLTAGE DIVIDERS 8 Claims, 9 Drawing Figs.

[52] US. Cl 338/120, 338/128, 338/142, 338/195 [51] Int. Cl Hlc /00 Field ofsearch 338/120, 195, 121, 122, 123, 129,126, 128, 138, 14 L [56] References Cited UNITED STATES PATENTS 2,241,615 5/1941 Plebanski 338/ X 338/ X 2,500,605 3/1950 De Lange et a1 frimary Examiner-Thomas J. Kozma AnorneyStowell & Stowell ABSTRACT: A layer resistance unit for voltage dividers adapted particularly for tuning or adjusting high frequency circuits capacitance diodes, said unit comprising series-connected main resistance elements at least some of which are connected in parallel with a side resistor and the latter being adapted to be varied so as to adjust the resistivity of the resistance unit to a desired characteristic, said main resistance elements and said side resistors being interconnected by conducting transverse or cross strips of conducting material. Said side resistors are adapted to have their resistance varied by progressively reducing the width of their current conductive layer surface. At least one main resistor having in addition to its side resistor connected to it in parallel a further layer resistance, all resistance layers of the unit i.e. main resistors, side resistors and parallel resistors having the same specific surface resistivity.

PATENTEU um] um 3602867 sum 1. OF 3 T 131 ISB M I liven/0r:

JOSEF KCSHLER ATTORNEYS PATENTED was] I971 SHEET 3 OF 3 'IIIIIII4 lnvenior: JOSEF KHLER 7 YZZZZUKQ A TORNEYS LAYER RESISTANCE UNIT FOR VOLTAGE mvnmns SPECIFICATION The invention relates to a layer resistance unit for ohmic voltage dividers in which the wiper current is very small and in which the predetermined voltage characteristic curve has to be maintained within very close tolerances. Such voltage dividers have wide and varied application in the measuring, control and communication technique. A comparatively new and large field of application is the tuning of high-frequency circuits having variable capacitance diodes (Varactors) in which the blocking voltage of these diodes is adjusted by means of such voltage dividers. For exactly calibrating the station scales of diode-tuned high-frequency receivers the same close or narrow tolerances of 1 to 2 percent are required for the voltage divider as for the hitherto customary tuning element, the rotary condenser. Such close tolerances cannot be maintained for layer resistors with the presently known methods since their stray or scatter values are still above 5 percent.

The basis of the invention is the provision of a layer resistance'element or unit which is economically producible in large series and which fulfills very high requirements regarding the fidelity of its characteristic curve.

' in accordance with the invention it is proposed for ohmic voltage dividers to provide a layer resistance element comprising sections formed by conducting cross strips, the sections being formed by a main resistance layer component or element and a side or shunt resistor, the latter being variable by variation of its current conducting layer area. These sections are, in accordance with the invention, adjusted by variation of their side resistors to the values given by the voltage characteristic curve in proportion to the total resistance. By this adjustment of the section resistance, the actual partial voltages on the cross strips can be made to coincide exactly with the desired or nominal voltages for these slide or wiper positions,

so that the actual characteristic curve coincides at least at these pointsexactly with the desired characteristic curve.

The invention starts from the premise, confirmed by practical experience, that the variations of the specific area resistivity of the layer over the entire region or at least over large partial regions, which cause the straying of the characteristic curve, run in one direction. Deviations from the characteristic curve in changing direction over very short partial stretches of the path of the wiper, which the concept of the invention cannot or but partly eliminate, do not at all occur or they occur in suchsmallvalues only with resistance layers suitable for such voltage dividers that they are inconsequential after the adjustment of the section resistances.

lt is known in step voltage dividers consisting of printed resistors, to correct the partial voltages of the individual steps by adjusting the individual resistors. Transferring these methods to continuous voltage dividers, i.e. in adjusting the resistor directly on the layer resistor, would inadmissably deform the voltage characteristic curve atthe adjusting places, if the adjustment is not carried out continuously and individually for each isingle resistor. Such an effort is however not bearable for mass? production and in most cases of application not even necessary. On the other hand, the subdivision of the resistance elements into layer sections remaining unchanged and adjustable side-resistors, in accordance with present invention, permits speedy determination and a sufficient elimination of the deviations of the characteristic curve by means of known, automatic adjustment methods suitable for in-series production.

For the solution of the present problem it has already been known to provide the layer resistance element of the voltage divider with an outer tap and, by means of a second voltage dithis method is likewise much too costly for mass production elements so as to remove once the stray values caused by the production, quite apart from the fact that it solves the problem for one point only of the characteristic curve and therefore but incompletely for many applications.

Although the reduction of the side resistors-such as by the application and the burning-in of conductive silver on its effective layer area-is within the four corners of this invention, use will be made in mass production of the known technique of increasing the resistance by partial removal of the resistance layer or scratching of insulating grooves into the resistance layer, respectively.

The number of sections into which the resistance element is subdivided, depends on the mechanical dimensions and the accuracy with which the adjustment is to be made. In general, a subdivision into three or four sections allows already to maintain close tolerances.

The ratio m of the sizes of the side resistors to its main resistance element is governed by the equation m=(q-h)/(q (h-l wherein q is the maximal factor of variation of the side resistor and h the thereby obtainable change of the sector resistance. For instance, with a side resistor being at first three times as large as the main resistance element, for its increase to twice its value, the section resistance may be increased to 1.143 times its value. Thevalues m and q are selected so that the thereby obtainable adjustment extends with certainty beyond the strayings of the section resistances, which are caused by the manufacture.

The adjustment itself is carried out in such a manner that at first the deviations of the section resistances from the desired or nominal values, given by the characteristic curve and the nominal resistance of the divider are measured, wherein simultaneously the section value having the largest plus deviation or the smallest minus deviation, respectively, for the case that no plus deviations have occurred, is determined. All remaining section resistances are then adjusted to this critical deviation by changing its side resistors, whereby the partial voltages on the cross strips reach the respective desired value.

If apart from the characteristic curve also the total resistance of the divider is to be held within very close limits-a condition which is not necessarily tied to the tolerance of the characteristic curve-one will fix the mean rough value of the resistance element so that also the highest stray values of the section resistances will lie below their desired values. in this case, all section resistances are adjusted to their desired value by changing their side resistors. Thus, not only the characteristic curve but also the total resistance of the divider are accurately adjusted.

In a first embodiment of the side resistor, the same is formed as a layer surface, the resistance value of which is increased for the purpose of adjustment by progressive reduction of its current carrying region. The layer area is in this case provided at one or both terminals with recesses or cutouts. For the adjustment, starting with one recess, a partial region is severed by progressively scratching an insulating groove approximately along a current flow line. In this method, the current carrying area is reduced in progressively increasing the resistance value.

In a further embodiment of the side resistor the same is formed as a layer area which is provided along one longitudinal side paralleling the current direction with a short circuit strip bridging a partial region. For adjusting, the short circuit strip is progressively severed from the resistance area by scratching an insulating groove, whereby the resistance is increased and the current carrying area of the resistor is decreased. For better use of the area and for lengthening the adjustment stretch, the layer areas of the side resistors may also be given 5- or meander-shape.

The formation of the resistance element in accordance with the present, invention is applicable to single-layer, linear dividers as well as to nonlinear dividers in which, in a known manner, the shape of the curve is obtained by the application of layers of different surface resistances. If the dimensions of the dividers permit, one will endeavor; in the interest of rational manufacture, to provide nonlinear characteristic curves also by layer elements having uniform specific surface resistance. For this purpose the layer area of the layer resistor is, in a known manner, made of different widths transversely to the current direction since, if there are not too great differences of width, up to about 1:5, the slope of the voltage curve is in a fair approximation inversely proportional to the width of the layer.

The subdivision of the resistance element into sections or sectors in accordance with the present invention permits the achievement of a further advantage in that only the slope variations within one section are represented by the change in width of the layer resistor, whereas the total slope of the section, i.e. the voltage drop between its boundary strips, in relation to the length of the path of the wiper between these strips is determined by a layer area wired in parallel, which may also be combined with the adjustable side resistor into one layer area. By this, voltage dividers may also be designed as normal resistance dividers having relatively great differences of slope of their characteristic curve which by means of known singlelayer elements could be designed as surface voltage dividers only. The change of the internal resistance as viewed from the wiper, occuring in passing through a strongly shunted surface section for obtaining small slopes, has no adverse effects in voltage dividers operating, in accordance with the starting point of the invention with practically unloaded wiper.

As long as the wiper contact moves on a cross strip, there occurs practically no voltage change since the resistance layer at this place is bridged by the conducting strip. The strips are therefore in the region of the path of the wiper kept as small as the manufacturing methods for the strips permit. Hereby the steps in the voltage characteristic curve are kept so small that they have in most cases no disturbing effect. For such cases of application in which even the smallest steps cannot be tolerated, a further embodiment is proposed in which the transverse strips are interrupted at the location at which they cross the path of the wiper. Hereby, the formation of steps in I the characteristic curve is largely avoided without impairing the parallel connection of the side resistors.

in accordance with an advantageous embodiment of the present invention all main side and parallel resistors are formed as resistance layer surfaces having equal specific surface resistivity. Hereby the advantages are achieved that all resistors may simultaneously be applied in one operation and thereby the manufacturing costs are kept low.

In a further embodiment of the present invention, the layer resistance element is applied, in a known manner, with an adjusting base-point and/or a series resistance, which are directly connected with the starting or the end connection, respective ly, of the voltage divider and which have preferably the same specific surface resistivity as the remaining resistors of the element. This has the advantage that all resistors connected with a constant voltage source are grouped together on a common carrier and that they therefore suffer equal temperature, humidity and aging changes which, on account of their proportionality, have but little effect on the voltage division.

ln accordance with a further improvement of the present invention, the side resistors to be adjusted are so arranged on the main resistance element that dividing lines to be applied for their adjustment are on a simple geometrical figure, preferably on a straight line or on the arc of a circle. By this, the movement of the chisel or stylus during the subsequent adjustment of the individual side resistors is substantially simplified providing a favorable prerequisite for the fully automatic adjustment of the side resistors.

The proposals in accordance with the present invention may be applied to voltage dividers with layer resistance elements of all known structural systems, such as rotary, slidable and spindle voltage dividers as well as multiple arrangements of the same.

Multiple voltage dividers are used on a large scale for channel memory aggregates for high-frequency receivers with diode tuning, in which the control voltages of the diodes are preadjusted for the selected channel frequency on the individual voltage dividers and are selectively switched on to the tuning diodes by mutually triggering switching devices.

In using the layer resistance elements according to the present invention for such multiple voltage dividers, it is suggested in accordance with a further embodiment of the present invention to connect the corresponding conducting transverse strips of the individual resistance elements with each other and to provide the thereby parallel-connected sections with common side resistor.

By this parallel-connection of the individual sections not only the adjustment of the multiple voltage dividers is essentially simplified but without additional effort it is also achieved that the voltage curves of the individual dividers coincide at least at the intersection points of the strips with the path of the wiper, whereby a very good assimilation of all curves among each other is achieved.

Apart from the common side resistors, common parallel re sistors may be used for adjustment of the slope as well as common base-pointand/or series-resistors. In such multiple systems all resistors of the element or unit are formed as layer resistance surfaces having equal specific surface resistivity so as to minimize the influence of temperature and humidity changes on the voltage division.

The common side-, paralleland base-point-resistors may on their part consist of individual layer surfaces connected in parallel or in series and may be arranged that the available surface is employed as advantageously as possible.

The layer resistance element in accordance with the present invention may also be employed in connection with a special form of ohmic voltage dividers in which several step voltages are continuously adjustable. Such voltage dividers comprise several step contacts at which partial voltages of the applied total voltage may be taken off, which on their part are again within certain ranges continuously adjustable. in a borderline case the ranges correspond to the step intervals and all the partial voltages are adjustable without interruptions. Such dividers are used, above all, where stepped voltages are needed but which, for adaption to possible straying or scattering of the user, are afterwards adjustable. One possibility of application of such voltage dividers has in recent times presented itself by a special method of tuning high-frequency circuits with variable capacitance diodes in high frequency receivers in which for the different channel frequencies predetermined voltages are needed, which are fixed by the desired characteristic curve of the capacitance diodes, which however for balancing of unavoidable diodes strayings or for intentional slight mistuning of the receiver should be variable within certain limits.

In a further embodiment of the present invention it is therefore proposed to assign to at least a part of the sections formed by the strips, preferably upon division into double groups each time to the second section, wipers which are adjustable continuously and independently of each other. The partial voltages which may be adjusted and picked-up by these wipers result in the step voltages which on their part may be selected by means of known devices, e.g. by a rotary step switch or a multiple push button switch with mutually releasing push buttons. A step voltage divider with uninterrupted adjustability of all partial voltages is obtained when each section of the resistance element is provided with an independent wiper and this wiper is connected to the stationary contacts of the step selector switch.

In many applications, the most favorable step adjustment range becomes smaller than the step interval. In this case, where according to the invention, independently of each other adjustable wipers are assigned each time to the second section of a double group division, whereas the intermediate sections remain free. These intermediate sections, which for exact maintenance of the step ranges have to have narrow tolerances, may likewise be adjusted, the same as the sections passed over by the wipers, by varying the side resistors coordinated to them. The adjustment may however be carried out in the section resistors themselves since they do not represent resistance strips the curvature of which could be impaired by the adjustment. Such voltage dividers finally may also be designed as a mixed form of both variations in which the individual sections provided with wipers follow each other directly whereas in part of the sections, for narrowing the step adjustment ranges as compared to the stepped intervals, intermediate resistors are interposed.

According to a further embodiment of the present invention it is proposed to form the resistance strips of the adjustable steps as annular segments and to pick up the step voltages adjusted on them from rotary contacts carrying the wipers and being arranged at the center of the strips. These contacts then form simultaneously the fixed contacts of the step selector wit h nd t r by e a le a av ng n the d ig of th device.

Also in this embodiment of the resistance element, the already proposed parallel resistors may be employed for forming nonlinear voltage. intervals adjustment ranges of different magnitude, respectively, of the individual steps by means of which the section voltages may be reduced to any desired degree. The parallel resistors may be formed in this case as individual separate layer surfaces or may be combined with'the side resistors to a single layer area. Moreover, in a specific embodiment of this proposal all resistors of the element are formed as layer surfaces having the same specific area resistivity so as to simplify manufacturing.

The geometric dimensions of the individual layer surfaces, the resistances of which are determined by the desired voltage intervals, adjustment ranges and the total resistance, are so chosen and arranged that, in consideration of the load capacity of the layer, the available space is well used and the dividing lines of the adjustable resistors are on a simple geometrical figure.

The proposals in accordance with the present invention permit rational manufacturing of ohmic voltage dividers having an accurate characteristic curve and present a significant advance n h echniqu of he e b ilding e ems The invention and its details are described in the following in connection with the drawings showing different examples of embodiment on an enlarged scale.

In the drawings:

FIG. I shows a layer resistance element for a voltage divider with rectilinear wiper movement;

FIG. 2 shows a partial, though modified, part of the element depicted in FIG. 1;

FIG. 3 shows the characteristic curve of a divider of FIGS. 1 an FIG. 4 shows a plan view of a layer resistance element for a voltage divider with circular wiper movement;

FIG. 5 shows the characteristic curve of the divider of FIG. 4;

FIG. 6 shows the resistance element for a quadruple voltage divider of a diode tuning aggregate;

FIG. 7 is a diagram of the characteristic curve of the voltage divider of FIG.

FIG. 8 shows a layer resistance element for a rotary step voltage divider with adjustable step voltages; and

FIG. 9 shows a wiring diagram for the individual partial resistors of the resistance element of FIG. 8.

As shown in FIG. 1, the initial connector A, the end connector E and the cross or transverse strips C, D, G of conducting silver are applied to or burned into a rectangular plate T of in- Sulating material. the strips dividing the element into the sections l to IV. Between the terminals A and E the main section or traclt resistors B, to B are applied as a homogeneous resistance layer with the specific surface resistivity p resistance of a square surface) on which by means of a symbolically shown wiper 5 any partial voltages u, of a total voltage 14,, applied at A and E may be picked up along the wiper, path or track 5. The strips C, D, G are kept in the region of the wiper path 5 so narrow that no disturbing step formation in the voltage curve occurs. Furthermore, within the individual sections the layer surfaces N, to N of the side resistors as well as in the sections I and II the layer surfaces P, and P of the parallel resistors of the same layer are applied. In section III the parallel resistors and the side resistors are combined into one surface. Except for the main resistors B, to B all resistors are formed as rectangular surfaces, the side resistor N consisting of three partial surfaces connected with bus bars in series.

The adjustment of the resistance element is effected by progressively scratching an insulating groove along the thin interrupted line into the side resistance surfaces whereby partial regions thereof are severed off and excluded from the current flow.

The resistance element or unit according to FIG. 1 is calculated and designed according to the heavy shown characteristic curve of FIG. 3, which is a usual curve for diode tuning in the ultra-short wave range, as will be explained more in details with reference to the attached Table 1.

Apart from normalized voltage curve of FIG. 3, the desired or nominal value of the total resistance r,,=200 K. is given. It is assumed that the maximal scatter of the unadjusted main resistances r,, consisting of the parallel-connected respective main resistance r,,, side resistance 1,, and, if any, the parallel resistance r,,, amounts maximally to 16 percent, which corresponds to a ratio of the maximal value to the minimal value of l.06:0.94=1.l28. For covering this stray or scatter range the factor q=3 and the ration m=4 is selected which, according to the equation m=(q-h)/(q(hl yields an adjustment range of h=l.l54 and therefore overlaps sufficiently the stray range. From the ratio m=4 follows furthermore that the value r, or 1 respectively, which designates the parallel connection of the main resistance r and the parallel resistance r,,, has to be 1.25 r, inasmuch as this value is reduced by the parallel connection to four times its value, i.e. 5 r, to the desired value of the parallel connection r,,.

Line I of Table 1 gives the percentage values of the voltages u to u on strip C, D, G or end terminal E, respectively, taken from the normalized characteristic curve of FIG. 3. From this follow the percentage values of the voltage drops Au, to Au of the total voltage, which are entered in line 2. For a wiper practically unloaded according to the premise, the same percentage values for the main resistances r,, obtain, which are entered in line 3. Line 4 shows the desired values of the main resistances r,, calculated for a total resistance of r,,=200 K. From this, by multiplication by the factor 1.25, the values for the parallel circuits r are obtained and entered in line 5.

The layer surfaces B, to B are designed corresponding to the increasing slope in the individual section, in accordance with known methods, with decreasing width and the resistance values in area units (p), resulting from their shape, are entered in line 6. From section IV in which, on account of the missing parallel resistor, the value is r,,=r,,, it follows from the conditions r,,,,=l09 K. (line 5) and r,, =3.24p (line 6) that value for the specific surface resistivity is p=33.6 K., this being valid also for all other layer areas. From this, the values for the other main resistors are calculated in K. and are entered in line 6.

The parallel resistances r, of sections I to III are determined from r (line 5) and r (line 6), which are entered in line 7. The lengths and widths, entered in line 8 and 9, obtain from the p values and from the available area space. The side resistances r,,, obtained from m-r,,, are entered in line 10 and their lengths and widths are entered in lines 1 l and I2.

Insulating grooves for adjusting the side resistors run parallel to the current lines in the sections so that two-thirds of the surface is severed upon scratching the entire length and thereby the resistance is increased to its triple value.

FIG. 2 shows a modified portion of section III of the element according to FIG. 1, in which the adjustment is demonstrated more in detail. The side resistor of this section consists of two section surfaces IIL, and the twice as long section surfaces N which are connected in series and which at first are bridged by a conductive strip K running along their longitudinal side. For adjustment, the conductor strip K is progressively severed along the broken line whereby the side resistance r,,,,, can be increased to three times its value.

FIG. 2 also shows the expedient serving to completely avoid the step formation in the characteristic curves at the cross strips. The strips D and G are for a short distance interrupted at their crossing points with the path s of the wiper, whereby the bridging of the resistance layer by the strip on the wiper path is eliminated and therefore a voltage change occurs during the movement of the wiper across these places.

For adjusting the resistance element, the four section resistances r,, are measured including the critical section, i.e. the section the resistance of which shows the largest plus deviation should occur, shows the smallest minus deviation, respectively. The other three section resistances are then brought to the critical deviation by increasing their side resistances so that their percentagewise share of the total resistance corresponds to the desired or nominal value. Thus, the desired voltages u, to u, are achieved also at the strips C, D, G.

In the present example it is assumed that the characteristic curve of the unadjusted element, as shown in FIG. 3 by a broken line, lies in the lower field of the tolerance and that the rough value of r shows the smallest negative percentage deviation, i.e. the critical deviation. This section remains therefore unchanged, whereas sections I, II, III, as shown by the heavy broken lines in the side resistors N, are increased to the same deviations.

The measurements could be carried out by means of the limit bridge and the adjustment by means of a hand engraving tool or cutter. For series-manufacturing one will use for this an electronically controlled device which memorizes the critical deviation and which scratches the insulating groove by a motor-driven cutter and stops the latter upon reaching the critical deviation.

The total resistance r will in this kind of adjustment show about the same scatter or stray as the unworked element, inasmuch as its lower limit is given by the condition that all the section resistances are nearly uniformly at the lower scatter limit and are therefore changed but little during adjustment. Its upper limit is then reached when the critical section resistance lies at the upper limit and the other section resistances have to be brought to this value.

In adjusting to the exact characteristic curve and the exact total resistance, the mean raw value of the element is lowered by lowering the specific surface resistance by 7 percent (at 6 percent scatter of the unworked element) so that no section resistance exceeds its desired value. This does away with the determination of the critical section resistance, since all sections have to be adjusted by increasing their side resistances to the desired value. Even the lowest scatter value, which amounts herein to 0.93X0.94=O.874, may be brought to the desired value by full adjustment.

In the same manner as the element according to FIG. 1, a layer resistance element having as support a cylinder surface may be designed. FIG. 1 would then show the cylinder surface developed in the plane of the drawing.

FIG. 4 shows a layer resistance element having a plane circular carrier and being provided for a rotary voltage divider. Its standardized or normalized voltage characteristic curve, shown in FIG. 5, has an exact exponential shape so that the section resistances as well as the slopes of its three equal sections I, II, III each increase by the same factor. This results in the same shape for its three main resistors B,, B,,, B,,,. The side resistances r,, are in this example larger at the ratio of n=3 than the main resistances and may be increased by severing off a partial region to the double value (q==2 This results in an adjustment range of h=1.l43 by which the scatter range ofi-o percent is also covered.

This element is calculated and designed in a similar manner as in the first example, wherein the side resistors and the parallel resistors are formed analogously as ring sectors. Apart from the three main resistors B,, B 3, it comprises the side resistors N,, N,, and the two-part side resistor N,,, as well as the first section of the parallel resistor P,. The adjustment of the side resistors is again done by scratching an insulating groove into the layer surfaces or the side resistors on a concentric circular path, shown by the broken lines, which has proved to be suitable for the construction of an automatic adjusting device.

To the starting terminal A there is connected a further layer surface F with the parallel-connected surface F and the base point terminal W, said layer surface F representing an adjustable base point resistance r, by which the voltage at terminal A is adjustable to an exact fraction of the total resistance. At the center of the element there is provided a central collector M, customary for rotary resistors, which serves as the countercontact for the wiper.

FIG. 6 shows a further example, in this case a resistance element for a quadruple voltage divider for a diode tuning aggregate, the individual dividers of which show a course of the curve per FIG. 7.

Four main resistor groups having the same specific surface resistivity are arranged on a carrier T of insulating material along the dot-and-dash line wiper paths s,,, s,,, s,, s., any partial voltages of a voltage applied to the starting terminal A and the end terminal E, may be picked up. Since the smallest adjustable divider voltage should, according to the diagram, amount to 3.6 percent of the total voltage U, the resistance surface F having the same specific surface resistivity as the main resistors is applied to the carrier T and connected with the starting terminal A, at which between the terminals W and A the so-called base point voltage of 3.6 percent drops.

The total resistance element is subdivided by the very narrow conducting transverse strips C, D into three sections I, II, III, wherein according to diagram of FIG. 7 the voltage on strip C should be 15 percent and on strip D 45 percent of the total voltage U. The main resistors B,, B B the reference signs of which are provided in FIG. 6 with the respective index a, b, c, a', of the voltage divider to which they belong are tapered in known manner in the direction of the wiper paths for producing within each section the slope variation of the voltage divider characteristic curve.

All main resistors of one section, e.g. the main resistors B,,,,,, B,,,,, B,,,,, B,,,,, have a common side resistor N,,, having the same specific resistivity as the main resistors, the resistance value of which before adjustment is four times as large as the resistance value of the four parallel-connected main resistors. By progressively severing off two-thirds of the width of the side resistor N the resistance value of the total section may, as extensively shown for the first embodiment, gradually be increased to 1.5154 times its value and thereby exactly adjusted.

For decreasing their total resistance so as to produce the predetermined voltage drop, parallel resistors P, and P respectively, are coordinated to the sections 1, II. The parallel resistors P, and P,, are applied for advantageous use of the surface, between the main resistors as three layer surfaces P P,. P, or P,, P,,.,, P each, and they have the same specific surfaces resistivity as the main resistors. The side resistors N, and N,,, which are coordinated to the sections 1 and II, are so dimensioned that they have four times the value of the parallel connection of the main and parallel resistors of the respective section. For advantageous use of the space, the side resistor N, is subdivided into two parallel-connected layer surfaces N,, and N All side resistors N N, N and N,,, are so arranged that their division lines are on a straight line and that the adjustment cutter may be brought into engagement by simple longitudinal displacement in all three sections.

The relatively small base point resistor F, which, likewise has the specific surface resistivity of the main resistors and which therefore is elongated and connected as its longitudinal sides, is adjusted by slitting the layer along the dotted line between the terminals A and W.

As a further example of an embodiment, FIG. 8 shows a layer resistance element for a rotary step voltage divider with continuously adjustable step voltages. FIG. 9 shows the wiring diagram for the individual partial resistors of this element.

The layer resistance element for this voltage divider is provided with four adjustable steps, in which the divider voltages of steps I to IV may selectively be taken off by contact arm Y rotatably supported at the center X of the carrier plate T. The pickup of these voltages is here done on the reverse side of the carrier plate at the end faces of contacts m, to m -which are rotatably supported at the center point of the resistance tracks B, to B,,- and which take off the voltages from the dot-anddash line wiper paths by means of the wipers S, to S The adjustment means for the wipers and the contact arm are not shown because they are not essential for the invention and may be presumed to be known.

The step divider should be designed so that a voltage U applied to its terminals A and E is each time lowered by dB and is variable in each step by the respective wiper continuously by :1 dB. The total resistance of the voltage divider should amount to 100 K. The loading of the wiper is assumed to be very small.

In accordance with these premises the subdivision of the layer resistance elements results in nine sections, the sections 1, II, III and IV comprising the resistance tracks and the sections 0, la, Ila, Illa and Na being fonned as intermediate resistors. The conducting connection of the main resistors B, the parallel resistors P and the side resistors N, which are provided with the corresponding section indices, can be gathered from the wiring diagram of FIG. 9. The transverse strips C, D, G, H, 1, L0 and V between the individual sections, consisting 'of conducting silver, are marked in FIG. 8 by inclined, close shading. All resistance surfaces consist of the same homogenous resistance layer with the specific surface re sistivity p (resistance of a square surface).

The adjustment of the sectional resistors is done in case of the sections 0, I, II, II and IV at the respective side resistors N to N,,- by progressively severing a part of the current conducting resistance surface along the dotted center line of these resistance surfaces.

The sections la, Ila and Illa which in each case consist of the intermediate resistors Z,, Z and Z, are adjusted by severing a partial region of these resistance surfaces. The dotted severing lines run so that upon complete adjustment about oneeighth of the current conducting layer surface is severed off, whereby the same percentagewise resistance increases is achieved as with the adjustment of the side resistors.

path of rotation is somewhat tapered from its beginning to its end resulting in a track resistance r of 5.25 p.

The calculation and the dimensioning of the further partial resistors of the layer resistance element is described by means of the attached Tables 2 and 3.

In line 1 the divider voltages in dB are entered for the four steps in accordance with the premises. From this follow the voltages at the transverse strips in percentages of the total voltage U applied at A and D, which are entered in line 2.

The partial voltages Au for each section are entered as percentages in line 3. The numerical values of the section resistances r entered as K. in line 4, coincide with the percentage values of line 2 inasmuch as the desired total resistance of the divider is 100 K. and the reaction of the very high consumer resistance on the voltage division may be neglected.

The ratio of the side resistances to the main resistances is selected as m=3 so that the main resistance r,, or the parallel connection r of the web resistance n, and parallel resistance r,,

The resistor of section IVa consists of 2 resistance surfaces Z,- and Z connected in series, the adjustment being alone at the surface Z The four resistance tracks B, to B are formed as annular sectors having a rotation range of 180. For linearizing the voltage course within the range of 2 dB, the surface along the has to be brought to the value For this follows for the main resistance in section IV a value of l.33 l3=17.3 K. whereby simultaneously the specific surface resistance of the entire resistance element is fixed at p=3.3 since the main resistances have a value of 5.25p, as shown above.

In line 5 are entered the values in Kohm taken from line 4 for the intermediate resistgs 2,, Z and Z, of tho sections la, Ila and Illa and herefrom their p-values are calculated. This determines the length and the width of these Z-layer surfaces entered in lines 6 and 7.

Since section 0 is provided with a side resistor, the value 8.9 K. has to be increased by the factor 1.33 to l 1.9 K. Its p-value is therefore 3.6 and the side ratio of its rectangular surface is consequently 1624.8.

The intermediate resistance of section IV=36.9 K., corresponding to 11.2p, is subdivided into two series-connected rectangular layer surfaces Z and 2,, the side ratios of which are so dimensioned that the total resistance amounts to l l.2p.

The r -values for sections 1, II and III, which are provided with parallel resistors, are calculated from the r,,-values by multiplication with 1.33 and are entered in line 8. The parallel resistances r,, follow from the condition that the parallel arrangement of the main resistance (17.3 K.) has to produce TABLE 1 For example per Fig. 1

Linel. Secti0n) I II III IV 1.. Ill-1v (percent of u 11.5 27. 5 56. 5 2 Aux-1v (percent of u 11. 5 16. 29. 43. 5 3 r. (percent of r.) 11.5 16. 29.- 43.5 4 r. (K ohm) 23.- 32. 58. 87." 5. rd (K ohm) 28. 8 40. 72. 5 109.

K ohm a K ohm a K ohm a- K ohm or 6 (K ohm, a) 1 115.- 3. 43 118. 3. 51 105. 3. 12 109. 3.24 7.-- r,,(Kohm,u-) 38.4 1.14 60.5 6. 5 8. P-length (mm.) 4. 56 9. P-width (mm.) 4. 10.- r, (K ohm, a). 115. 3. 43 160. 13. 11. N-length (mm). 11.5 30.- 12 N-width (mm.) 3. 4 2. 3

TABLE 2 Sections) 0 I Ia II IIa.

\Ialues 20=e1 15=l=1 oltage u (percent) on cross strip. C Section voltage A u (percent) 8.9 Section resistance r, (K ohm) 8.9

Z-resistance (K9, 0) 11. 9

Z-area mean length 1.

r resistances (KS). 11) P-area, mean length l rn resistances (K9, 0') N-area, mean length l rd resistances (K12) P-arca. mean Width b.

Narea, mean width b Linel, Sections- III Illa IV IVs 1'.......... Dbvalucs 3:1 i1 1L. oltage 11 (percent) on cross strip. L 35.0 an. 1 03.1 E 100 -3 Section voltage A u (percent) 14. o 13.0 530.0 4... Section resistnnccsrflKfl)... 7. 14.6 3.0 36.9

5 Z-resistancc (Ktlaa) r 14.6 4.4 36.9 11.2 6 Z-area, mean length l 25. r T Z-area, mean width b 4 5. 7

8. rs resistances (K9) 9.7

. Tn resistances (Kna.) 22.1

10 P-area, mean length I...

11... P-aroa, mean Width b 12 rn resistances (Knee) 29. 1

13 N-area, mean length l.v

The resistance of section IV (36.9K9 and 11.20, resp.) is divided into two series-connected rectangle areas Zrv and Z, having a ratio oi their sides 35:5.8 (=60) and 1312.5 (=5.2a) respectively.

with the r, resistance each time the r value. The K. and p values of the three parallel resistors P,, P and P, are entered in line 9 and their lengths and widths are specified in lines 10 and 11.

By multiplication of the r -resistances (or the r -resistance in section IV, respectively) by the factor m=3 yields the side resistance r, which are entered in line 12. The mean lengths and widths are calculated from their p-values and are entered in lines 13 and 14.

By corresponding increase of the side resistors N to N or of the intermediate resistors Z, to Z respectively, the sectional resistances may be adjusted to a deviation :L2 percent of their desired value r,,. Thereby, the desired voltages of the steps and their adjustment ranges are maintained with a tolerance 10.2 dB.

lclaim:

l. ln a layer resistance uhit for nonlinear diiriiidvoig dividers, in which the divisional voltage is picked up by a wiper moving across a layer track,

a. a wiper,

b. a plurality of series connected main resistors, of layer construction and in tandem relationship, positioned on an insulating base, said main resistors being of nonuniform width, said wiper movable across said main resistors,

c. at least one side resistor, of layer construction, connected in parallel with each said main resistor, said side resistors having severing lines to thereby admit of the removal of portions with consequent increase in electrical resistance path of travel of said wiper.

thereof,

a conducting cross-strip between each of the said main resistors and extending across and contacting the entire width of said main resistors except for an interruption at its intersection with the path of travel with said wiper, layer resistance material extending through said interruption, said side resistors connected between adjacent cross-strips to effect said parallel connection,

e. the length of the cross-strips being greater than the width of the main or side resistors. 2. The layer resistance unit of claim 1 wherein the width of 3. The layer resistance element of claim 1 wherein at least one of said main resistors has, in addition to its side resistance,

connected in parallel a further layer resistance.

4. The layer resistance of claim 1 wherein the said side resistors are comprised of material having the same specific surface resistivity as said main resistors.

5. The layer resistance unit of claim 1 wherein said severing lilies are straight lines.

6. The layer resistance unit of claim 1 wherein said severing lines are segments of a circle.

7. The layer resistance unit of claim 1 wherein said main resistors are shaped as annular segments.

8. The layer resistance unit of claim 1 including a second wiper, independently adjustable of said first wiper on said main resistors. 

1. In a layer resistance unit for nonlinear ohmic voltage dividers, in which the divisional voltage is picked up by a wiper moving across a layer track, a. a wiper, b. a plurality of series connected main resistors, of layer construction and in tandem relationship, positioned on an insulating base, said main resistors being of nonuniform width, said wiper movable across said main resistors, c. at least one side resistor, of layer construction, connected in parallel with each said main resistor, said side resistors having severing lines to thereby admit of the removal of portions with consequent increase in electrical resistance thereof, d. a conducting cross-strip between each of the said main resistors and extending across and contacting the entire width of said main resistors except for an interruption at its intersection with the path of travel with said wiper, layer resistance material extending through said interruption, said side resistors connected between adjacent cross-strips to effect said parallel connection, e. the length of the cross-strips being greater than the width of the main or side resistors.
 2. The layer resistance unit of claim 1 wherein the width of the cross-strips is smallest adjacent their intersection with the path of travel of said wiper.
 3. The layer resistance element of claim 1 wherein at least one of said main resistors has, in addition to its side resistance, connected in parallel a further layer resistance.
 4. The layer resistance of claim 1 wherein the said side resistors are comprised of material having the same specific surface resistivity as said main resistors.
 5. The layer resistance unit of claim 1 wherein said severing lines are straight lines.
 6. The layer resistance unit of claim 1 wherein said severing lines are segments of a circle.
 7. The layer resistance unit of claim 1 wherein said main resistors are shaped as annular segments.
 8. The layer resistance unit of claim 1 including a second wiper, independently adjustable of said first wiper on said main resistors. 